Combined oral contraceptives and mental health: Are adolescence and the gut-brain axis the missing links?

Combined oral contraceptives (containing synthetic forms of estradiol and progestins) are one of the most commonly used drugs among females. However, their effects on the gut-brain axis have not been investigated to a great extent despite clear evidence that suggest bi-directional interactions between the gut microbiome and endogenous sex hormones. Moreover, oral contraceptives are prescribed during adolescence, a critical period of development during which several brain structures and systems, such as hypothalamic-pituitary-gonadal axis, undergo maturation. Considering that oral contraceptives could impact the developing adolescent brain and that these effects may be mediated by the gut-brain axis, further research investigating the effects of oral contraceptives on the gut-brain axis is imperative. This article briefly reviews evidence from animal and human studies on the effects of combined oral contraceptives on the brain and the gut microbiota particularly during adolescence.

Effects of pair-housing pubertal and adult male and female mice on LPS-induced age-dependent immune responses: A potential role for the gut microbiota.

Puberty is a critical period of development that is marked by the maturation of the stress and immune systems. There are marked age and sex differences in peripheral and central inflammatory responses to an immune challenge between pubertal and adult mice. Given the strong link between the gut microbiome and immune system, it is possible that the age and sex differences in immune responses are mediated by age and sex differences in gut microbial composition. The current study investigated whether cohousing adult and pubertal CD1 mice through three weeks of pair-housing, with the potential for microbiome exchange via coprophagy and other close contact, could mitigate age-dependent immune responses. Cytokine concentrations in the blood and cytokine mRNA expression in the brain were assessed following exposure to the immune challenge lipopolysaccharide (LPS). The results show that all mice displayed increased cytokine concentrations in serum and central cytokine mRNA expression in the hippocampus, hypothalamus and prefrontal cortex (PFC) at eight hours following LPS treatment. Pubertal male and female mice, that were pair-housed with a pubertal counterpart, displayed lower cytokine concentrations in serum and lower cytokine mRNA expression in the brain compared to adult mice that were pair-housed with an adult counterpart. However, when adult and pubertal mice were pair-housed, the age differences in both peripheral cytokine concentrations and central cytokine mRNA expression were mitigated. We also found that pair-housing adult and pubertal mice eliminated the age difference in gut bacterial diversity. These results suggest that microbial composition could be involved in modulating these age-associated immune responses and thus may represent a potential therapeutic target.

Pubertal consumption of R. badensis subspecies acadiensis modulates LPS-induced immune responses and gut microbiome dysbiosis in a sex-specific manner.

Puberty is a critical period of development characterized by significant brain remodeling and increased vulnerability to immune challenges. Exposure to an immune challenge such as LPS during puberty can result in inflammation and gut dysbiosis which may lead to altered brain functioning and psychiatric illnesses later in life. However, treatment with probiotics during puberty has been found to mitigate LPS-induced peripheral and central inflammation, prevent LPS-induced changes to the gut microbiota and protect against enduring behavioural disorders in a sex-specific manner. Recent findings from our laboratory revealed that pubertal R. badensis subspecies acadiensis (R. badensis subsp. acadiensis) treatment prevents LPS-induced depression-like behavior and alterations in 5HT1A receptor expression in a sex-specific manner. However, the underlying mechanism remains unclear. Thus, the aim of this study was to gain mechanistic insights and to investigate the ability of R. badensis subsp. acadiensis consumption during puberty to mitigate the effects of LPS treatment on the immune system and the gut microbiome. Our results revealed that pubertal treatment with R. badensis subsp. acadiensis reduced sickness behaviors in females more than males in a time-specific manner. It also mitigated LPS-induced increases in pro-inflammatory cytokines in the blood and in TNFα mRNA expression in the prefrontal cortex and the hippocampus of female mice. There were sex-dependent differences in microbiome composition that persisted after LPS injection or R. badensis subsp. acadiensis consumption. R. badensis subsp. acadiensis had greater impact on the microbiota of male mice but female microbiota's were more responsive to LPS treatment. This suggested that female mice microbiota's may be more prone to modulation by this probiotic. These findings emphasize the sex-specific effects of probiotic use during puberty on the structure of the gut microbiome and the immune system and highlight the critical role of gut colonization with probiotics during adolescence on immunomodulation and prevention of the enduring effects of infections.

Enduring sex-dependent effects of lipopolysaccharide treatment on the hypothalamic-pituitary-gonadal axis in mice.

Pubertal stress causes enduring sexual behavior dysfunction in males and females, but the underlying mechanism remains unknown. These changes may arise from pubertal programming of the hypothalamic-pituitary-gonadal axis. Previous findings show that stress exposure downregulates the hypothalamic-pituitary-gonadal axis, particularly through the reduction of the neuropeptide kisspeptin (Kiss1) and its receptor (Kiss1R). Although acute changes in kiss1 and Kiss1r genes have been observed following pubertal immune stress, it is unclear whether immune stress-induced downregulation of kiss1 and kiss1r persists beyond puberty. The current study investigated the enduring sex-specific consequences of lipopolysaccharide on the expression of Kiss1 and Kiss1r in 160 pubertal or adult mice at multiple time points. Six-week and 10-week-old male and female mice were treated with either saline or with lipopolysaccharide. Mice were euthanized either 8 h or 4 weeks following treatment. Although we did not identify any sex differences, our results revealed that lipopolysaccharide treatment decreases hypothalamic Kiss1 and Kiss1r in both pubertal and adult mice within 8 h of treatment. The decreased hypothalamic Kiss1 expression persists 4 weeks later only in mice treated with lipopolysaccharide during puberty. Our findings highlight the age-dependent vulnerability of the hypothalamic-pituitary-gonadal axis to immune stress, providing a better understanding of the mechanisms implicated in allostatic shift during immune stress. Finally, our findings also show the effects of immune stress on various components of the hypothalamic-pituitary-gonadal axis, which could have implications for sexual and fertility-related dysfunctions.

The regulatory roles of progesterone and estradiol on emotion processing in women.

Emotion processing is known to interact with memory. Ovarian steroid hormones, such as progesterone and estradiol, modulate emotion processing and memory. However, it is unclear how these hormones influence brain activity when emotion processing is integrated with working memory (WM). Therefore, the objective of this study was to examine the relationship between endogenous hormonal concentration and brain activity during emotion processing in the context of a WM n-back task in 74 young women using functional magnetic resonance imaging (fMRI). Results show that positive emotion processing activates reward-related areas, such as the caudate and putamen, whereas negative emotion processing activates a corticolimbic network, including the amygdala and hippocampus. Furthermore, our findings provide evidence that progesterone modulates more bottom-up brain activation during both positive and negative emotion processing, whereas estradiol activates lateralized, top-down regulation. These findings provide insight on the neural correlates of emotion processing during an n-back task in young women and highlight how important it is to consider women's endogenous hormonal concentration in neurobiological and cognition research.

Programming Effects of Pubertal Lipopolysaccharide Treatment in Male and Female CD-1 Mice.

Puberty is a critical period of development marked by sexual, immune, and neural maturation. Exposure to stress during this period can lead to enduring changes in brain functioning and in behavior; however, the underlying mechanisms and the programming effects of stress during puberty remain unknown. Therefore, the objective of this study was to investigate the programming effects of pubertal immune challenge in response to a homotypic stressor later in life in CD-1 mice. Age and sex differences in the peripheral and central cytokine levels, along with sickness behavior and telemetry data, were analyzed following the secondary treatment. The results showed that pretreatment with LPS attenuated the immune response to a second homotypic challenge. Males pretreated with LPS during puberty and in early adulthood displayed an attenuated hypothermic response following the second LPS treatment compared with saline-pretreated controls, which is consistent with the attenuated peripheral IL-6 and IFN-γ concentrations. Females pretreated with LPS during puberty displayed lower IL-1ß, TNF-α, and IL-6 mRNA expression in the prefrontal cortex following the secondary immune challenge compared with saline controls. The results of this study show that exposure to LPS during puberty programs the peripheral and central immune responses, resulting in an attenuated immune response following a subsequent homotypic stressor. Thus, exposure to an immune challenge during puberty affects immune function later in life, which could permanently affect brain function and have implications on mental health.

Neurotoxicity and Underlying Mechanisms of Endogenous Neurotoxins.

Endogenous and exogenous neurotoxins are important factors leading to neurodegenerative diseases. In the 1980s, the discovery that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) contributes to Parkinson's disease (PD) symptoms led to new research investigations on neurotoxins. An abnormal metabolism of endogenous substances, such as condensation of bioamines with endogenous aldehydes, dopamine (DA) oxidation, and kynurenine pathway, can produce endogenous neurotoxins. Neurotoxins may damage the nervous system by inhibiting mitochondrial activity, increasing oxidative stress, increasing neuroinflammation, and up-regulating proteins related to cell death. This paper reviews the biological synthesis of various known endogenous neurotoxins and their toxic mechanisms.

Oral contraceptive use, especially during puberty, alters resting state functional connectivity.

Millions of women worldwide use oral contraceptives (OCs), often starting during puberty/adolescence. It is, however, unknown how OC use during this critical period of development affects the brain. The objective of the current study was to examine resting state functional connectivity (FC) in the default mode network (DMN), central executive network (CEN), salience network (SN), reward network (RN), and subcortical limbic network of the brain using independent component analysis (ICA) between pubertal- and adult-onset OC users (n = 27) and naturally cycling women (n = 48). It was hypothesized that OC use would result in network-specific increases and decreases in FC and that pubertal-onset OC use would result in differences to the aforementioned networks compared to adult-onset OC use. Pubertal-onset OC use is related to heightened FC in the SN compared to adult-onset OC users. In general, OC use also increases connectivity in the SN, CEN, RN, and subcortical limbic network compared to NC women. No significant differences in connectivity were observed in the DMN between OC users and NC women. These findings provide a mechanistic insight for the altered executive functioning and emotion/reward processing previously seen in OC users, which may then increase their vulnerability to mental health conditions.

Adolescent social instability stress leads to immediate and lasting sex-specific changes in the neuroendocrine-immune-gut axis in rats.

Social instability stress (SS; daily 1 h isolation and change of cage partner from postnatal day (P) 30-45) in adolescence produces elevations in corticosterone during the procedure in male and female rats, but no lasting changes in hypothalamic-pituitary-adrenal (HPA) responses to psychological stressors, although deficits in social and cognitive function are evident in adulthood. Here we investigated the effects of SS in corticosterone response to an immune challenge (lipopolysaccharide, LPS, 0.1 mg/kg), on gene expression in the hippocampus, and on gut microbiota, when tested soon- (P46) or long- (P70) after SS. The temporal pattern of corticosterone release after LPS differed between SS and control rats irrespective of the time since SS exposure in females, whereas in males, SS did not alter corticosterone release after LPS. Expression of genes in the hippocampus relevant to immune and HPA function differed between saline-treated SS and control rats depending on sex and time tested, but with lasting consequences of SS in both sexes. LPS-treatment altered hippocampal gene expression, with bigger effects of LPS evident in control than in SS female rats, and the opposite in male rats. Further, effects sometimes depended on the age at time of LPS treatment. SS and control rats differed in both fecal and colon microbiome composition in all but P46 males, and stress history, sex, and age influenced the effects of an immune challenge on the gut microbiome. In sum, adolescent stress history has consequences for immune function into adulthood that may involve effects on the gut microbiome.

Use of the birth control pill affects stress reactivity and brain structure and function.

Millions of women worldwide use oral contraceptives (i.e., birth control pill; OCs), often starting during puberty/adolescence; however, it is unknown how OC use during this critical period of development affects the brain, especially with regard to emotional working memory. Here, we examined stress reactivity, and brain structure and function in OC users using the Trier Social Stress Test and structural and functional magnetic resonance imaging (MRI). Our results show that OC use during puberty/adolescence gives rise to a blunted stress response and alters brain activation during working memory processing. OC use, in general, is also linked to increased prefrontal brain activation during working memory processing for negatively arousing stimuli. OC use is also related to significant structural changes in brain regions implicated in memory and emotional processing. Together, these findings highlight that OC use induces changes to brain structure and function and alters stress reactivity. These findings may provide a mechanistic insight for the increased vulnerability to mood-related mental illness in women after OC use.

Probiotics in Treatment of Viral Respiratory Infections and Neuroinflammatory Disorders.

Inflammation is a biological response to the activation of the immune system by various infectious or non-infectious agents, which may lead to tissue damage and various diseases. Gut commensal bacteria maintain a symbiotic relationship with the host and display a critical function in the homeostasis of the host immune system. Disturbance to the gut microbiota leads to immune dysfunction both locally and at distant sites, which causes inflammatory conditions not only in the intestine but also in the other organs such as lungs and brain, and may induce a disease state. Probiotics are well known to reinforce immunity and counteract inflammation by restoring symbiosis within the gut microbiota. As a result, probiotics protect against various diseases, including respiratory infections and neuroinflammatory disorders. A growing body of research supports the beneficial role of probiotics in lung and mental health through modulating the gut-lung and gut-brain axes. In the current paper, we discuss the potential role of probiotics in the treatment of viral respiratory infections, including the COVID-19 disease, as major public health crisis in 2020, and influenza virus infection, as well as treatment of neurological disorders like multiple sclerosis and other mental illnesses.

Effect of Heavy Ion 12C6+ Radiation on Lipid Constitution in the Rat Brain.

Heavy ions refer to charged particles with a mass greater than four (i.e., alpha particles). The heavy ion irradiation used in radiotherapy or that astronauts suffer in space flight missions induces toxicity in normal tissue and leads to short-term and long-term damage in both the structure and function of the brain. However, the underlying molecular alterations caused by heavy ion radiation have yet to be completely elucidated. Herein, untargeted and targeted lipidomic profiling of the whole brain tissue and blood plasma 7 days after the administration of the 15 Gy (260 MeV, low linear energy (LET) = 13.9 KeV/µm) plateau irradiation of disposable 12C6+ heavy ions on the whole heads of rats was explored to study the lipid damage induced by heavy ion radiation in the rat brain using ultra performance liquid chromatography-mass spectrometry (UPLC-MS) technology. Combined with multivariate variables and univariate data analysis methods, our results indicated that an orthogonal partial least squares discriminant analysis (OPLS-DA) could clearly distinguish lipid metabolites between the irradiated and control groups. Through the combination of variable weight value (VIP), variation multiple (FC), and differential (p) analyses, the significant differential lipids diacylglycerols (DAGs) were screened out. Further quantitative targeted lipidomic analyses of these DAGs in the rat brain tissue and plasma supported the notion that DAG 47:1 could be used as a potential biomarker to study brain injury induced by heavy ion irradiation.

Probiotic consumption during puberty mitigates LPS-induced immune responses and protects against stress-induced depression- and anxiety-like behaviors in adulthood in a sex-specific manner.

Puberty/adolescence is a significant period of development and a time with a high emergence of psychiatric disorders. During this period, there is increased neuroplasticity and heightened vulnerability to stress and inflammation. The gut microbiome regulates stress and inflammatory responses and can alter brain chemistry and behaviour. However, the role of the gut microbiota during pubertal development remains largely uninvestigated. The current study examined gut manipulation with probiotics during puberty in CD1 mice on lipopolysaccharide (LPS)-induced immune responses and enduring effects on anxiety- and depression-like behaviours and stress-reactivity in adulthood. Probiotics reduced LPS-induced sickness behaviour at 12 h in females and at 48 h following LPS treatment in males. Probiotics also reduced LPS-induced changes in body weight at 48 h post-treatment in females. Probiotic treatment also prevented LPS-induced increases in pro- and anti-inflammatory peripheral cytokines at 8 h following LPS treatment, reduced central cytokine mRNA expression in the hypothalamus, hippocampus and PFC, and prevented LPS-induced changes to in the gut microbiota. A single exposure to LPS during puberty resulted in enduring depression-like behaviour in female mice, and anxiety-like behaviour in male mice in adulthood. However, pubertal exposure to probiotics prevented enduring LPS-induced depression-like behaviour in females and anxiety-like behaviors in males. Moreover, probiotics altered toll-like receptor-4 activity in the paraventricular nucleus of the hypothalamus (PVN) in males in response to a novel stressor in adulthood. Our results suggest that the gut microbiome plays an important role in pubertal neurodevelopment. These findings indicate that exposure to probiotics during puberty mitigates inflammation and decreases stress-induced vulnerabilities to emotional behaviours later in life, in a sex-specific manner.

Effect of LPS treatment on tyrosine hydroxylase expression and Parkinson-like behaviors.

Puberty is a critical period of development during which the brain undergoes reorganizing and remodeling. Exposure to stress during this period is thought to interfere with normal brain development and increase susceptibility to mental illnesses. In female mice, pubertal exposure to lipopolysaccharide (LPS), a bacterial endotoxin, has been shown to alter sexual, anxiety-like, and depression-like behaviors and cognition in an enduring manner. However, the mechanisms underlying these effects remain unknown. The present study examined age and sex difference in tyrosine hydroxylase (TH) expression and dopamine-dependent and Parkinson-like behaviors following LPS treatment. The results show that LPS treatment during adulthood causes an enduring increase in TH expression in many of the brain regions examined. In contrast, there is no change in TH expression following LPS treatment during puberty. However, pubertal LPS treatment induces enduring behavioral deficits in tests of Parkinson-like behaviors, more so in male than in female mice. These results suggest that the low levels of TH following exposure to pubertal immune challenge may predispose mice to Parkinson-like behavior. These findings add to our understanding of stress and immune responses during puberty and their impact on mental health later in life.

Age and sex differences in immune response following LPS treatment in mice.

Puberty is an important developmental event that is marked by the reorganizing and remodeling of the brain. Exposure to stress during this critical period of development can have enduring effects on both reproductive and non-reproductive behaviors. The purpose of this study was to investigate age and sex differences in immune response by examining sickness behavior, body temperature changes, and serum cytokine levels following an immune challenge. The effects of circulating gonadal hormones on age and sex differences in immune response were also examined. Results showed that male mice display more sickness behavior and greater fluctuations in body temperature following LPS treatment than female mice. Moreover, adult male mice display more sickness behavior and a greater drop in body temperature following LPS treatment compared to pubertal male mice. Following gonadectomy, pubertal and adult males displayed steeper and prolonged drops in body temperature compared to sham-operated counterparts. Gonadectomy did not eliminate sex differences in LPS-induced body temperature changes, suggesting that additional factors contribute to the observed differences. LPS treatment increased cytokine levels in all mice. However, the increase in pro-inflammatory cytokines was higher in adult compared to pubertal mice, while the increase in anti-inflammatory cytokines was greater in pubertal than in adult mice. Our findings contribute to a better understanding of age and sex differences in acute immune response following LPS treatment and possible mechanisms involved in the enduring alterations in behavior and brain function following pubertal exposure to LPS.

Environmental Enrichment Cage for Laboratory Mice: A Downloadable Alternative.

Environmentally enriched housing (EE) provides a stimulating and species-typical environment that enhances brain plasticity and cognition, while reducing disease severity in laboratory animals. However, standardizing EE protocols has been challenging due to issues such as variability, high pricing, or limited laboratory space. To address these challenges, we present a replicable and cost-efficient cage protocol that is accessible to researchers with limited resources and space constraints. The protocol is designed to provide a stimulating and species-typical environment for the animals. It incorporates elements such as social interaction, physical exercise, cognitive stimulation, manipulable objects, environmental variability, and sensory stimulation. As evidenced in our previous studies using our protocol, users can expect to observe similar neuroplastic and health-wise benefits that accompany EE experimental paradigms. These included straightforward step-by-step guide, which allows for construction of functional EE cages in under 8 hr. Basic knowledge of 3D printing and laser cutting is required, but no advanced skills are necessary. The protocol enables researchers to create stimulating and replicable environments that promote animal welfare, enhance brain plasticity, and yield valuable experimental results for low cost. © 2024 Wiley Periodicals LLC. Basic Protocol: An effective and cost-efficient environmental enrichment cage designed to encourage standardization amongst laboratory protocols.

Psychobiotics and the Microbiota-Gut-Brain Axis: Where Do We Go from Here?

The bidirectional relationship between the gut microbiota and the nervous system is known as the microbiota-gut-brain axis (MGBA). The MGBA controls the complex interactions between the brain, the enteric nervous system, the gut-associated immune system, and the enteric neuroendocrine systems, regulating key physiological functions such as the immune response, sleep, emotions and mood, food intake, and intestinal functions. Psychobiotics are considered tools with the potential to modulate the MGBA through preventive, adjunctive, or curative approaches, but their specific mechanisms of action on many aspects of health are yet to be characterized. This narrative review and perspectives article highlights the key paradigms needing attention as the scope of potential probiotics applications in human health increases, with a growing body of evidence supporting their systemic beneficial effects. However, there are many limitations to overcome before establishing the extent to which we can incorporate probiotics in the management of neuropsychiatric disorders. Although this article uses the term probiotics in a general manner, it remains important to study probiotics at the strain level in most cases.

Enduring influence of pubertal stressors on behavioral response to hormones in female mice.

This article is part of a Special Issue "Puberty and Adolescence". The pubertal period is a time of change in an animal's response to stress, and it is a second period of sexual differentiation of the brain. Recently, it was discovered that particular stressors during the prolonged pubertal period of female mice result in enduring changes in behavioral responsiveness of the brain to estradiol and progesterone. Depending on the behavior, pubertal immune challenge or shipping from suppliers may decrease, eliminate, or even reverse the effects of estradiol. Pubertal immune challenge results in changes in the number of estrogen receptor-immunoreactive cells in key brain areas suggesting a cellular mechanism for this remodeling of the brain's response to hormones. A hypothesis is put forward that predicts that particular adverse experiences in girls may cause long-term alterations in the brain's response to estradiol and/or progesterone via activation of the immune system. This could lead to mood disorders or altered response to any behavior influenced by estradiol in humans.

The sex-dependent and enduring impact of pubertal stress on health and disease.

Illness is often predicated long before the manifestation of its symptoms. Exposure to stressful experiences particularly during critical periods of development, such as puberty and adolescence, can induce various physical and mental illnesses. Puberty is a critical period of maturation for neuroendocrine systems, such as the hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-adrenal (HPA) axes. Exposure to adverse experiences during puberty can impede normal brain reorganizing and remodelling and result in enduring consequences on brain functioning and behaviour. Stress responsivity differs between the sexes during the pubertal period. This sex difference is partly due to differences in circulating sex hormones between males and females, impacting stress and immune responses differently. The effects of stress during puberty on physical and mental health remains under-examined. The purpose of this review is to summarize the most recent findings pertaining to age and sex differences in HPA axis, HPG axis, and immune system development, and describe how disruption in the functioning of these systems can propagate disease. Lastly, we delve into the notable neuroimmune contributions, sex differences, and the mediating role of the gut microbiome on stress and health outcomes. Understanding the enduring consequences of adverse experiences during puberty on physical and mental health will allow a greater proficiency in treating and preventing stress-related diseases early in development.